A drug used for decades to treat liver disease appears to slow down the progression of Parkinson’s disease, according to tests in fruit flies.

Researchers say the findings support the fast-tracking of the drug, ursodeoxycholic acid (UDCA), for a clinical trial in Parkinson’s patients.

A mutation in the LRRK2 gene is the single most common inherited cause of Parkinson’s disease. However, the precise mechanism that leads to Parkinson’s is still unclear.

For the study, published in the journal Neurology, researchers demonstrated the beneficial effects of the drug in vivo using the fruit fly (Drosophila melanogaster). In fruit flies, the mitochondrial defects caused by the LRRK2 mutation to dopaminergic neurons can be monitored through the progressive loss of visual function. Flies carrying the mutation maintained their visual response when fed with UDCA.

“The treatment of fruit flies carrying the faulty LRRK2 gene with UDCA showed a profound rescue of dopaminergic signaling. Feeding the flies with UDCA partway through their life slows the rate at which the fly brain then degenerates,” says Chris Elliott from the University of York’s biology department, who collaborated on the study.

“Whilst we have been looking at Parkinson’s patients who carry the LRRK2 mutation, mitochondrial defects are also present in other inherited and sporadic forms of Parkinson’s, where we do not know the causes yet,” says Oliver Bandmann, professor of movement disorders neurology at the University of Sheffield. “Our hope is therefore that UDCA might be beneficial for other types of Parkinson’s disease and might also show benefits in other neurodegenerative diseases.”

Defects in mitochondria, and as a consequence reduced energy levels, are a factor in a number of diseases that affect the nervous system, including Parkinson’s and motor neuron disease. Nerve cells have a particularly high energy demands, therefore defects in the cell’s energy generators will crucially affect their survival.

“Following on from the promising results of our in vitro drug screen, we were keen to further investigate and confirm the potential of UDCA in vivo—in a living organism. UDCA has been in clinical use for decades and thus could be advanced to the clinic rapidly if it proves beneficial in clinical trials,” says Bandmann.

Parkinson’s UK, the Wellcome Trust, and the Norwegian Parkinson Foundation funded the work.